Motile cilia (also interchangeably called “flagella”) are conserved organelles extending from the surface of many animal cells and play essential functions in eukaryotes, including cell motility and environmental sensing. Large motor complexes, the ciliary dyneins, are present on ciliary outer-doublet microtubules and drive movement of cilia. Ciliary dyneins are classified into two general types: the outer dynein arms (ODAs) and the inner dynein arms (IDAs). While ODAs are important for generation of force and regulation of ciliary beat frequency, IDAs are essential for control of the size and shape of the bend, features collectively referred to as waveform. Also, recent studies have revealed unexpected links between IDA components and human diseases. In spite of their importance, studies on IDAs have been difficult since they are very complex and composed for several types of IDA motors, each unique in composition and location in the axoneme. Thanks in part to genetic, biochemical, and structural analysis of Chlamydomonas reinhardtii, we are beginning to understand the organization and function of the ciliary IDAs. In this review, we summarize the composition of Chlamydomonas IDAs particularly focusing on each subunit, and discuss the assembly, conservation, and functional role(s) of these IDA subunits. Furthermore, we raise several additional questions/challenges regarding IDAs, and discuss future perspectives of IDA studies.

中文翻译：

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莱茵衣藻纤毛内动力蛋白臂亚基的组成和功能研究

运动纤毛（也可互换称为“鞭毛”）是从许多动物细胞表面延伸的保守细胞器，在真核生物中发挥重要功能，包括细胞运动和环境感应。大的运动复合体，即纤毛动力蛋白，存在于纤毛外双微管上并驱动纤毛的运动。纤毛动力蛋白分为两种一般类型：外动力蛋白臂 (ODA) 和内动力蛋白臂 (IDAs)。虽然 ODA 对于产生力和调节纤毛跳动频率很重要，但 IDA 对于控制弯曲的大小和形状至关重要，这些特征统称为波形。此外，最近的研究揭示了 IDA 成分与人类疾病之间的意想不到的联系。尽管它们很重要，对 IDA 的研究一直很困难，因为它们非常复杂，并且由几种类型的 IDA 马达组成，每种马达在轴丝中的组成和位置都是独一无二的。部分归功于基因、生化和结构分析莱茵衣藻，我们开始了解睫状体 IDA 的组织和功能。在这篇综述中，我们总结了衣藻IDA 的组成，特别关注每个亚基，并讨论了这些 IDA 亚基的组装、保护和功能作用。此外，我们提出了一些关于 IDA 的额外问题/挑战，并讨论了 IDA 研究的未来前景。